The invention relates to an adhesive composition comprising a water based component containing a film-forming polymer and a particulate thermoplastic component. The adhesive composition is useful either as a one-shot bookbinding adhesive or as a primer composition in a two-shot bookbinding method.
Description of Related Art
In the manufacture of book blocks, either a xe2x80x9cone-shotxe2x80x9d method or a xe2x80x9ctwo-shotxe2x80x9d method is employed. In the one-shot method, a hot melt adhesive composition (i.e., a one-shot adhesive) is applied directly onto the spine of the book block. In the two-shot method, however, a primer composition is first applied onto the spine as the xe2x80x9cfirst shotxe2x80x9d. Then, an adhesive composition (i.e., a second-shot adhesive) is applied to the surface of the dried primer as the xe2x80x9csecond shotxe2x80x9d. Either water based compositions or hot melt compositions can be used as primer compositions and/or the second-shot adhesive compositions with typically water based compositions being used as primer compositions and hot melt compositions as second-shot adhesive compositions.
Water based primer compositions exhibit better penetration into the signatures (grouping of sheets of paper) due to their longer open times and low viscosities. They are also less susceptible to fluctuations in temperature once the book is constructed. However, water based primers also set more slowly because of the time needed to evaporate the water contained therein. Hence, the maximum bookbinding manufacturing speed is limited by the time needed to dry and set the water based primers. Dryers and heat are often utilized to facilitate drying of the water based primers in order to maintain reasonable production rates. When exposed to intense heat, however, the water based primer coating tends to skin over and trap moisture within the formed polymeric membrane. The trapped water in the interior of the water based primer layer vaporizes causing the membrane to lift and form large blisters that break and burn under heat. On the other hand, the water based primer coating that is not sufficiently dried also causes splattering and blistering upon application of a second-shot hot melt adhesive at application temperatures ranging from about 100xc2x0 C. to about 200xc2x0 C. due to remaining water present in the water based primer. The blistered layer of the water based primer is not bonded to the book block, and thus results in voids along the book spine and within the set adhesive layers. Partially bound books are not only defective products that can""t be sold, but also may cause jams and delays in the bookbinding process itself.
U.S. Pat. No, 4,536,012 discloses a two-shot continuous bookbinding process using a water based primer composition and a hot melt adhesive. The water based primer composition comprises a polymeric latex and ungelatinized starch having a granule size of about 2-150 microns. The granule starch complexes a major portion of the water contained in the primer composition during the drying stage, thereby resisting blistering and charring when exposed to high drying temperatures.
U.S. Pat. No. 4,702,496 further discusses the use of ungelatinized starch in water based primer compositions which are utilized with a hot-covering adhesive in order to eliminate the need for the drying step.
U.S. Pat. No. 4,960,295 discloses two-shot hot melt bookbinding adhesives including a first-shot hot melt adhesive as the primer and a second-shot hot melt adhesive as the cover glue. The primer is based on ethylene-vinyl acetate (EVA) polymers having a low viscosity. The second-shot adhesive is based on EVA polymers having a higher viscosity.
In one aspect, the invention features an adhesive composition comprising a water based component containing a film-forming polymer and a thermoplastic component selected from the group consisting of thermoplastic polymers, thermoplastic resins, hot melt adhesive compositions, and mixtures thereof. The thermoplastic component is in particulate form having a mean particle size of from about 10 microns to about 1,500 microns.
In another aspect, the invention features a method of making the aforesaid adhesive composition comprising grinding a thermoplastic component to the desired particle size and mixing the particles of the thermoplastic component with a water based component and optional additives.
In yet another aspect, the invention features a method of binding a book block having a spine area to form a book comprising applying the aforesaid adhesive composition to a book block spine, drying the adhesive composition, and applying a second-shot hot melt bookbinding adhesive to the surface of the dried adhesive composition.
In yet another aspect, the invention features a method of binding a book block having a spine area to form a book comprising applying the aforesaid adhesive composition to a book block spine, heating the adhesive composition such that the water based component forms a dried film and that the thermoplastic component melts, and adhering a book cover or a capping paper with the book block by means of the thermoplastic component.
The invention is an improvement over traditional water based bookbinding primer compositions by the addition of a particulate thermoplastic component. The particulate thermoplastic component advantageously improves the interfacial adhesion between the water based primer and the second-shot hot melt adhesive, particularly when employing a particulate hot melt adhesive composition as the thermoplastic component. The thermoplastic component also inhibits or delays the formation of a polymeric membrane barrier upon rapid loss of water, thereby eliminating the formation of large blisters. Further, the adhesive composition can be formulated to have a substantially increased solids content while maintaining a sufficiently low viscosity. The increased solids content increases the rate of set of the adhesive composition as a primer, thereby speeding up the production rate.
The adhesive composition of the invention finds particular utility for use as a primer composition that is applied to a substrate, such as the spine of a book block, and dried, and then, a second-shot hot melt adhesive is applied to the surface of the dried primer. In this instance, the adhesive composition of the invention can be formulated to exhibit 180xc2x0 peel strength increase of at least 20%, and preferably, at least 30%. That is, the interfacial adhesion between the adhesive composition of the invention as the primer and the sequentially applied second-shot hot melt adhesive is improved by at least 20%, preferably at least 30% in comparison to the interfacial adhesion between the same primer composition lacking the particulate thermoplastic component and the second-shot hot melt adhesive.
The adhesive composition can also be formulated as a second-shot adhesive used in the two-shot bookbinding method in combination with any primer compositions including the adhesive composition of the invention formulated as a primer composition.
The adhesive composition also finds particular utility for use as a one-shot bookbinding adhesive that is applied to a substrate such as the spine of a book block, and then heated such that the particulate thermoplastic component becomes molten. In this instance, the adhesive composition of the invention exhibits the combined advantages of better penetration into the signatures (grouping of sheets of paper) contributed by the water based component as well as improved rate of set of the adhesive and specific adhesion contributed by the particulate thermoplastic component.